JP3938050B2 - Driving circuit for active matrix light emitting device - Google Patents

Driving circuit for active matrix light emitting device Download PDF

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Publication number
JP3938050B2
JP3938050B2 JP2002574645A JP2002574645A JP3938050B2 JP 3938050 B2 JP3938050 B2 JP 3938050B2 JP 2002574645 A JP2002574645 A JP 2002574645A JP 2002574645 A JP2002574645 A JP 2002574645A JP 3938050 B2 JP3938050 B2 JP 3938050B2
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Prior art keywords
light emitting
emitting element
line
switching element
tft
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JPWO2002075713A1 (en
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博之 中村
茂樹 近藤
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キヤノン株式会社
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Priority to PCT/JP2002/002592 priority patent/WO2002075713A1/en
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    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/30Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
    • G09G3/32Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
    • G09G3/3208Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
    • G09G3/3225Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED] using an active matrix
    • G09G3/3233Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED] using an active matrix with pixel circuitry controlling the current through the light-emitting element
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007Display of intermediate tones
    • G09G3/2018Display of intermediate tones by time modulation using two or more time intervals
    • G09G3/2022Display of intermediate tones by time modulation using two or more time intervals using sub-frames
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2300/00Aspects of the constitution of display devices
    • G09G2300/08Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
    • G09G2300/0809Several active elements per pixel in active matrix panels
    • G09G2300/0842Several active elements per pixel in active matrix panels forming a memory circuit, e.g. a dynamic memory with one capacitor
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2300/00Aspects of the constitution of display devices
    • G09G2300/08Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
    • G09G2300/0809Several active elements per pixel in active matrix panels
    • G09G2300/0842Several active elements per pixel in active matrix panels forming a memory circuit, e.g. a dynamic memory with one capacitor
    • G09G2300/0852Several active elements per pixel in active matrix panels forming a memory circuit, e.g. a dynamic memory with one capacitor being a dynamic memory with more than one capacitor
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2300/00Aspects of the constitution of display devices
    • G09G2300/08Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
    • G09G2300/0809Several active elements per pixel in active matrix panels
    • G09G2300/0842Several active elements per pixel in active matrix panels forming a memory circuit, e.g. a dynamic memory with one capacitor
    • G09G2300/0861Several active elements per pixel in active matrix panels forming a memory circuit, e.g. a dynamic memory with one capacitor with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2330/00Aspects of power supply; Aspects of display protection and defect management
    • G09G2330/02Details of power systems and of start or stop of display operation

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a driving circuit for a light-emitting element used in an image display device, specifically, an organic and inorganic electroluminescence (hereinafter referred to as “EL”) element, a light-emitting diode (hereinafter referred to as “LED”), and the like. The present invention relates to a drive circuit for an active matrix light-emitting element that drives and controls a self-light-emitting element, and an active matrix display panel using the same.

[0002]
[Prior art]
A display that combines organic and inorganic EL light-emitting elements or light-emitting elements such as LEDs in an array and displays characters using a dot matrix is widely used in televisions, portable terminals, and the like.
[0003]
In particular, these displays using self-luminous elements are attracting attention because they have features such as a wide viewing angle and no backlight for illumination unlike displays using liquid crystals. Above all, an active matrix type display that performs static driving by combining a transistor or the like with these light emitting elements has higher brightness, higher contrast, and higher definition than a simple matrix driving display that performs time division driving. Have been gaining attention in recent years.
[0004]
Regarding the organic EL element, analog gradation method, area gradation method, and time gradation method can be cited as well as the conventional method for producing gradation in an image.
[0005]
(1) As an analog type conventional example, an example of a display element having two thin film transistors (hereinafter referred to as TFTs) per pixel, which is the simplest, with respect to an active matrix driving light emitting element is shown in FIGS . In FIG. 4 , 101 is an organic EL element, 102 and 103 are TFTs, 107 is a scanning line, 108 is a signal line, 109 is a power supply line, 110 is a ground potential, and 111 is a memory capacity using a capacitor.
[0006]
The operation of FIG. 4 will be described below. When the TFT 102 is turned on by the scanning line 107, the video data voltage from the signal line 108 is accumulated in the memory capacity 111. Even when the scanning line 107 is turned off and the TFT 102 is turned off, the gate electrode of the TFT 103 is Since the voltage is continuously applied, the TFT 103 is kept on.
[0007]
On the other hand, the source electrode of the TFT 103 is connected to the power supply line 109, the drain electrode is connected to one electrode of the light emitting element, and the video data voltage of the drain electrode of the TFT 102 is input to the gate electrode. The amount of current between the electrodes is controlled by the video data voltage. At this time, the organic EL element 101 is disposed between the power line 109 and the ground potential, and emits light according to the amount of current.
[0008]
The amount of current flowing at this time depends on the gate voltage of the TFT 103, and the current characteristic is changed in an analog manner by using a region (saturation region) in which the source current characteristic (Vg-Is characteristic) rises with respect to the gate voltage. Is changing.
[0009]
As a result, the light emission luminance of the organic EL element which is a light emitting element is controlled, and display can be performed including gradation. This gradation expression method is called an analog gradation method because it is performed using an analog video data voltage. In this case, on the drive signal side, it is necessary to change the gamma (γ) characteristic on the video data signal side in accordance with the voltage-luminance characteristic of the organic EL element.
[0010]
Similarly to liquid crystal display elements and CRTs, light emitting elements can display gray scales with varying brightness of each pixel in order to display moving images on computer terminals, personal computer monitors, televisions, etc. It is also advantageous to obtain the compatibility. In addition, the drive system is simplified, which is advantageous in terms of cost.
[0011]
Currently used TFTs include amorphous silicon (a-Si) and polycrystalline silicon (p-Si) methods, but they can be miniaturized with high mobility, and progress in laser processing technology. Therefore, the specific gravity of the polycrystalline silicon TFT is increased from the viewpoint that the manufacturing process can be performed at a low temperature. However, in general, a polycrystalline silicon TFT is easily affected by the grain boundary that constitutes the TFT, and in particular, the Vg-Is current characteristic tends to vary greatly from TFT element to TFT element in the saturation region. Therefore, even if the video signal voltage input to the pixels is uniform, there is a problem that display unevenness occurs.
[0012]
In general, many of the current TFTs are simply used as switching elements, and a region in which the gate voltage considerably higher than the threshold voltage of the transistor is applied and the relationship of the drain voltage to the source voltage is constant (this is called a linear region). Therefore, the variation in the saturation region is less likely to occur.
[0013]
(2) Area gradation method On the other hand, the area gradation method is proposed in documents AM-LCD2000 and AM3-1. In this method, one pixel is divided into a plurality of sub-pixels, each sub-pixel is turned on / off, and gradation is expressed by the area of the pixel that is turned on.
[0014]
In such a usage method, since the gate voltage of the TFT is much higher than the threshold voltage and can be used in the linear region where the relationship of the drain voltage to the source voltage is constant, the TFT characteristics are also stable. The light emission luminance of the light emitting element is also stable. In this system, each element is controlled on and off, emits light at a constant luminance without producing a light and shade, and controls gradation according to the area of the sub-pixel to emit light. This is called an area gradation method.
[0015]
However, in this method, only digital gradations depending on the subpixel division method can be obtained, and in order to increase the number of gradations, the area of the subpixels must be reduced and the number of subpixels must be increased. However, even if the transistor is miniaturized using a polycrystalline silicon TFT, the area of the transistor portion arranged in each pixel erodes the area of the light emitting portion, and the light emission luminance of the display panel is reduced to reduce the pixel aperture ratio. Results in lowering. Therefore, when the aperture ratio is increased, the gradation is lowered, and brightness and gradation are in a trade-off relationship, and as a result, it is difficult to increase the gradation.
[0016]
(3) Time gradation method In the time gradation method, the gradation is controlled by the light emission time of the organic EL element, which is reported in 2000SID 36.4L.
[0017]
FIG. 5 is an example of a circuit diagram of one pixel portion of a conventional display panel adopting a time gray scale method. In FIG. 5 , 101 is an organic EL element, 102 to 104 are TFTs, 107 is a scanning line, 108 is a signal line, 109 is a power supply line, 110 is a ground potential, 111 is a memory capacity, and 112 is a reset line.
In the time gray scale method using this circuit configuration, when the TFT 103 is turned on, the organic EL element 101 emits light with the highest luminance due to the voltage from the signal line, and then the TFT 103 is appropriately timed within one field time by the TFT 104. In this method, the gradation is displayed according to the light emission time.
[0018]
In this method, the light emission time is adjusted by selecting a plurality of light emission periods. For example, when displaying 8 bits (256 gradations), the light emission time ratio is selected from eight subfield periods of 1: 2: 4: 8: 16: 32: 64: 128. . Then, immediately before each subfield period, since light emission or non-light emission in that subfield is selected, there is an addressing period for the scanning lines of all pixels each time. After the addressing period ends, the display panel is caused to emit light entirely by changing the voltage of the power supply line 109 all at once.
[0019]
Therefore, since the display is basically not performed during the addressing period, the effective light emission period within one field is as follows when N-bit gradation display is performed.
Effective light emission period = (1 field period) − (1 screen addressing period × N)
It becomes. Therefore, the light emission time is relatively shortened, and the light emission amount of the display panel is reduced for the observer.
[0020]
For this reason, it is necessary to increase the light emission amount per subfield to compensate for the light emission amount in the entire field, but this requires increasing the light emission luminance of each light emitting element, which reduces the life of the light emitting element. Connected. In addition, in a normal liquid crystal display (LCD), it is necessary to address only the number of gradation bits where one addressing is required per field, so a higher-speed addressing circuit is required and the power consumption is increased. Is inevitable.
[0021]
[Problems to be solved by the invention]
An object of the present invention is to provide a novel circuit configuration of a pixel transistor for a novel active matrix light-emitting element, and to provide a display panel that is superior to the conventional one, in order to improve the above-described conventional technology. There is.
[0022]
The present invention for solving the above problems, the scanning lines, on the substrate signal line and the reset line is provided, the driving of the light-emitting elements crossing arranged in the vicinity of said signal line and the reset line and the scanning line A circuit,
A constant current source connected to the drive power supply;
A second switching element arranged in series with the constant current source;
A light emitting element arranged in series with the constant current source and the second switching element;
A first switching element disposed in series with the constant current source and the second switching element and disposed in parallel with the light emitting element;
A thin film transistor having a gate electrode connected to the scan line, a source electrode connected to the signal line, and a drain electrode connected to a control terminal of the first switching element; A first memory circuit comprising a memory capacity connected to the control terminal;
A thin film transistor having a gate electrode connected to the scan line, a source electrode connected to the reset line, and a drain electrode connected to a control terminal of the second switching element; A second memory circuit comprising a memory capacity connected to the control terminal;
Have
When a scanning selection signal is input to the scanning line, each thin film transistor of the first and second memory circuits is turned on, and the signal voltage of the signal line and the reset voltage of the reset line are set to the first and second. In addition to accumulating in each memory capacity of the memory circuit,
The second switching element is turned on by the reset voltage, the current to the light emitting element is determined by turning the first switching element on or off according to the signal voltage,
Driving the light emitting element characterized in that the current to the light emitting element is cut off regardless of whether the first switching element is on or off by turning off the second switching element by the voltage of the reset line. Circuit .
[0023]
In the driving circuit of the present invention, the first switching element is preferably a first thin film transistor including three electrodes of a source, a drain, and a gate.
[0024]
The drive circuit of the present invention includes a preferred embodiment having a memory circuit capable of storing video data signals. In other words, the driving circuit of the present invention has a memory circuit including a gate electrode connected to a scanning line, a second thin film transistor having a source electrode and a drain electrode connected to a signal line, and a first memory capacitor. Is one of the preferred embodiments of the present invention.
[0025]
Further, the drive circuit according to the present invention preferably includes an on / off control using the above drive circuit configuration. That is, the driving circuit of the present invention controls on / off of the light emitting element by controlling the current flowing through the first switching element and the amount of current flowing through the light emitting element in accordance with information from the scanning line and the signal line. Is one of the preferred embodiments of the present invention.
[0026]
Further, the present invention includes a preferable embodiment in which gradation display is performed using the above drive circuit configuration. A time gray scale method or an analog gray scale method may be used. That is, the driving circuit of the present invention which performs gradation display by controlling the light emission time by turning on and off the light emitting element is one of the preferred embodiments of the present invention, and also according to information from the scanning line and the signal line. Thus, the drive circuit of the present invention that controls the emission brightness of the light emitting element by controlling the amount of current flowing through the first switching element and the amount of current flowing through the light emitting element is also a preferred embodiment of the present invention. is there.
[0027]
In particular, it is preferable to control on / off of the light emitting element by switching the second switching element. More preferably, the second switching element is a third thin film transistor including three electrodes of a source, a drain, and a gate. Also, the second switching element having a second memory circuit composed of a fourth thin film transistor and a second memory capacity and having an output from the memory circuit connected to the gate electrode of the third thin film transistor is disposed. The drive circuit of the present invention is also preferable.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
The main thing of this invention exists in the drive circuit structure of the novel active matrix type light emitting element which has arrange | positioned the switching element electrically in parallel with respect to the light emitting element.
[0029]
According to the configuration of the present invention, on / off of the first switching means is controlled by the signals from the scanning line and the signal line, and when the first switching means is in the off state, or to the light emitting element side by current distribution. In addition, the light emitting element can emit light over a period in which current flows , and the on / off state of the light emitting element can be controlled by the second switching means . Hereinafter, the present invention will be described by showing specific embodiments, but the present invention is not limited thereto.
[0030]
FIG. 1 is a circuit diagram of one element portion of the light emitting element of the present invention.
[0031]
11 is an organic EL element which is a light emitting element, 12 is a second TFT, 13 and 26 are first and third TFTs corresponding to the first and second switching means of the present invention, 16 is a constant current source, 15 is a scanning line, 14 is a video data signal line, 17 is a power supply line, 18 is a first power supply (ground potential in this figure), 19 is a memory capacity, and 20 is a second power supply (ground potential GND in this figure). , 24 are fourth TFTs, and 25 is a second memory capacity .
[0032]
Here, both the first power source 18 and the second power source 20 show the ground potential, but other potentials may be independently used.
[0033]
In the present circuit, the light emitting element 11 is always connected to a power supply line 17 connected to a driving power supply (not shown), a constant current source 16 and a first power supply 18 that follow the power supply line 17, and the light emitting element and first switching means. The current between the constant current source and the ground potential is distributed according to the conductance of the TFT 13, and light emission with a predetermined luminance is obtained from the light emitting element according to the amount of the current.
[0034]
Hereinafter, an operation example of this circuit configuration will be shown.
[0035]
First, a scanning line selection signal is input from the scanning line 15 to the second TFT 12 and the fourth TFT 24. At this time, a low level voltage, which is a light emission signal of the light emitting element, is applied to the signal line 14 and accumulated in the memory capacitor 19, and the TFT 13 is turned off. As a result, the conductance of the light emitting elements arranged in parallel becomes smaller.
[0036]
On the other hand, a high level signal voltage is applied to the reset line 23 in order to turn on the third TFT 26, and at the same time, it is accumulated and held in the memory capacitor 25.
[0037]
Under this condition, the current from the constant current circuit flows to the light emitting element, and a predetermined light emission luminance can be obtained according to the conductance of the TFT 13 and the light emitting element.
[0038]
On the contrary, when a high level signal voltage is applied to the signal line and the TFT 13 becomes low resistance (on state), no current flows through the light emitting element regardless of whether the TFT 26 is on or off, and no light is emitted. Further, in order to turn off the light emitting element, the current from the constant current source can be cut off only by turning off the TFT 26. Therefore, the light emitting element cannot be lit regardless of the state of the TFT 13.
[0039]
It should be noted that the magnitude of the video data signal needs to be inversely related to the light emission luminance characteristics of the light emitting element, and it is necessary to perform inverse gamma (γ) correction by a correction circuit that generates the video data signal. There is.
[0040]
Therefore, it is necessary to newly provide a correction circuit for the video data signal, and the current from the constant current source always flows through either the light emitting element 11 or the TFT 13 when the third TFT 26 is on. For constant current sources, the same current always flows. This is disadvantageous in that the current consumption is larger than that of the light emitting element that does not consume current in the conventional non-light emitting state.
[0041]
However, when ON / OFF is repeated instantaneously, even if a constant current source is used, a transient time is required until the current stabilizes, and a desired light emission brightness cannot be obtained during this time. The response speed of this circuit is more advantageous. The constant current source, a third TFT26 is necessarily always continues to flow a constant current when the ON state, in terms of current stability it is preferred circuit of the present invention.
[0042]
On the other hand, it is desirable that the characteristics required for the TFT 13 be as high as possible as compared with the conductance of the light emitting element when the light emitting element is turned on. However, when the light emitting element is turned off, it is necessary to concentrate the current on the TFT 13 side, and ideally, the current flowing through the light emitting element needs to be zero. It is necessary to use a TFT whose resistance is low enough to pass only a current less than the threshold.
[0043]
As an example of the digital gradation method currently used in computers and the like, consider the case where each element performs a gradation gradation display of 256 gradations. If the light emission time is constant, the light emission luminance is proportional to the amount of current flowing through the element. If the current amount indicating the maximum luminance in the light emission state is 1, the current amount of the minimum luminance is 1/256. It is only necessary to control the conductance of the TFT so that less current flows through the non-light emitting element. Even if the current amount in the non-light-emitting state is set to 1/5 of the minimum luminance current amount, it is understood that the on / off ratio of the TFT 13 is about 1: 1000, and an on / off ratio of only three digits is sufficient.
[0044]
Therefore, as far as the on / off ratio is concerned, the transistor required for the TFT 13 used in the circuit of the present invention is different from that of a general polycrystalline silicon TFT that requires an on / off ratio of about 4 to 6 digits. The property is very loose. With such characteristics, it is highly probable that even a TFT using a recent organic semiconductor can be used, and it can be said that the circuit configuration is very promising .
[0045]
FIG. 2 is a layout diagram in which the circuit configuration of FIG. 1 is applied to a matrix panel.
[0046]
Further, by controlling on / off of the TFT 26, it becomes possible to perform time gradation display. This operation will be described in FIG. 1 and FIGS.
[0047]
FIG. 3 shows a timing chart in the case of performing time gradation by controlling a light emission time within one frame period using a light emitting element provided with a driving circuit of the present invention.
[0048]
In FIG. 3 , A1 to A4 indicate address periods of each subfield. Within the A1 period, scanning signals are sequentially applied from the scanning lines X = 1 to n arranged in a matrix. Within each scanning period, on / off signals of pixels from Y = 1 to m are sequentially applied from the signal line, and each pixel starts to emit light. A period indicated by E1 to E4 is a light emission period of each subfield, and these are called PWM control light emission periods.
[0049]
In this case, the lighting time in one frame is divided into subfield periods having lengths of 1/2, 1/4, 1/8, and 1/16, respectively, and it is controlled whether to turn on in that period. For example, a pixel for obtaining a light emission luminance of 1/2 is lit only in a subfield period of 8 lengths of scanning line selection time (address period).
[0050]
When a scan selection signal is input to the scanning line 15 in FIG. 1 during the address period in FIG . 3 , the TFT 12 and TFT 24 are turned on, and this state is maintained by the memory capacitors 19 and 25 for a predetermined period. The period in which the TFT 24 is on is an address period, and is a period for determining information of one subfield. At this time, a low level voltage (light emission signal) or a high level voltage (non-light emission signal) is input from the video data control circuit 22 to each signal line 14 in order from the left signal line of the light emitting panel, for example. The state of the TFT 13 of each pixel is determined. Immediately after this, each light emitting element to which the light emission signal is input starts to emit light.
[0051]
In the next subfield period, the next reset voltage is applied to the TFT 24 from the reset line, and at the same time, a light emission signal or a non-light emission signal is applied to each signal line as in the previous subfield, and the next subfield period. The state is maintained over
[0052]
In this example, an ON signal is output from the video data control circuit 22 to the signal line 14 in the first address period of one frame in which the scanning line is selected, and a period of 1/2 (in this case, 1 / frame of 1 frame). (Time 2) The light emitting element emits light. By turning off in the address period corresponding to the remaining period, the viewer can see 50% light emission luminance.
[0053]
Here, a general example in which both the first power source 18 and the second power source 20 are set to the ground potential is shown, but other potentials may be used as a matter of course. However, when different potentials are used, it is necessary to provide another power supply line in the matrix wiring, which makes the light emitting element panel complicated.
[0054]
If the signals input to the video data signal lines 14 and 23 have a high level and a low level, the signal transmission in the light emitting element panel is less affected by noise and the operation is stabilized. Since it is possible to operate at a low voltage by lowering the applied voltage level, higher-speed signal transmission is possible.
[0055]
Further, by using the driving circuit of the present invention, the light emission luminance can be changed in an analog manner to obtain a grayscale. For example, since the difference in conductance between the on and off states of the light emitting element is about 3 digits, the conductance range of the TFT 13 is made with the same about 3 digits, and the conductance of the light emitting element and the TFT 13 shown in FIG. If the distribution of the amount of current from the constant current source 16 is changed, the emission luminance can be freely controlled. For example, if the same amount is distributed, the current amount of the light emitting element is ½, and a luminance showing 50% gradation can be obtained.
[0056]
It is needless to say that a transistor satisfying the above performance is not limited to an amorphous silicon or polysilicon TFT, and is not dependent on a TFT constituent material because it is a sufficiently possible characteristic even with an organic TFT using a recent organic semiconductor. .
[0057]
【The invention's effect】
As described above, a novel pixel circuit for an organic EL element can be configured by using a configuration of a small number of pixel transistors. Furthermore, when time gradation is performed, the light emission time becomes longer, and the luminance of the light emitting panel can be improved.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of one pixel portion showing an embodiment of the present invention.
2 is a circuit diagram showing a matrix arrangement of the display panel having the pixel configuration of FIG.
FIG. 3 is a timing chart when time gray scale is performed on a display panel having a driving circuit of the present invention.
FIG. 4 is a circuit diagram of one pixel portion of a conventional active matrix light emitting device.
FIG. 5 is a circuit diagram of one pixel portion showing another embodiment of a conventional active matrix light emitting device.

Claims (1)

  1. A driving circuit for a light emitting element disposed on a substrate provided with a scanning line, a signal line, and a reset line, in the vicinity of an intersection of the scanning line, the signal line, and the reset line,
    A constant current source connected to the drive power supply;
    A second switching element arranged in series with the constant current source;
    A light emitting element arranged in series with the constant current source and the second switching element;
    A first switching element disposed in series with the constant current source and the second switching element and disposed in parallel with the light emitting element;
    A thin film transistor having a gate electrode connected to the scan line, a source electrode connected to the signal line, and a drain electrode connected to a control terminal of the first switching element; A first memory circuit comprising a memory capacity connected to the control terminal;
    A thin film transistor having a gate electrode connected to the scan line, a source electrode connected to the reset line, and a drain electrode connected to a control terminal of the second switching element; A second memory circuit comprising a memory capacity connected to the control terminal;
    Have
    When a scanning selection signal is input to the scanning line, each thin film transistor of the first and second memory circuits is turned on, and the signal voltage of the signal line and the reset voltage of the reset line are set to the first and second. In addition to accumulating in each memory capacity of the memory circuit,
    The second switching element is turned on by the reset voltage, the current to the light emitting element is determined by turning the first switching element on or off according to the signal voltage,
    Driving the light emitting element, wherein the current to the light emitting element is cut off regardless of whether the first switching element is on or off by turning off the second switching element by the voltage of the reset line circuit.
JP2002574645A 2001-03-21 2002-03-19 Driving circuit for active matrix light emitting device Expired - Fee Related JP3938050B2 (en)

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JP2001080504 2001-03-21
JP2001080504 2001-03-21
PCT/JP2002/002592 WO2002075713A1 (en) 2001-03-21 2002-03-19 Drive circuit for driving active-matrix light-emitting element

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CN1265339C (en) 2006-07-19
CN1460239A (en) 2003-12-03

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